The Role of Zinc Finger Genes in Leukemogenesis: The objective of the proposed study is to understand normal hematopoiesis and the malignant transformation of hematopoietic cells by identifying the biological functions of Ikaros proteins. Ikaros is essential for normal hematopoiesis and T cell differentiation and acts as a tumor suppressor. The Ikaros gene is alternately spliced to generate multiple zinc finger proteins involved in gene regulation and chromatin remodeling. Our preliminary data show that: 1) Ikaros is phosphorylated at multiple evolutionarily conserved sites by CK2 and other kinases during G1 and S phase of the cell cycle 2) Phosphorylation of Ikaros at specific amino acids regulates its DNA-binding ability and subcellular localization. 3) Ikaros binds to the Bcl-xL gene promoter in vivo and disregulation of Ikaros activity is associated with upregulation of Bcl-xL gene expression. The specific aims of our proposals are: Specific Aim #1: Determine how site-specific CK2-mediated phosphorylation contributes to Ikaros'tumor suppressor activity by controlling its function as a regulator of differentiation and cell cycle progression. We hypothesize that phosphorylation of Ikaros interferes with its function in transcriptional regulation and chromatin remodeling and influences cellular proliferation. We will define the role of Ikaros phosphorylation at CK2 target sites in the chromatin remodeling of Ikaros target genes. The role of Ikaros'phosphorylation in regulating T cell differentiation and T cell proliferation will be studied in vivo. Murine stem cells from mice with targeted disruption of Ikaros will be infected with retroviral vectors containing wild type Ikaros or phosphomimetic Ikaros mutants and transplanted into sublethally irradiated Ikaros knockout mice. The ability of phosphomimetic Ikaros mutants to restore normal T cell differentiation will be compared to that of wild type Ikaros. Specific aim #2: Dissect the mechanism of CK2- Ikaros-mediated regulation of Bcl-xL expression and its contribution to Ikaros function as a tumor suppressor. Previous studies suggest that Ikaros represses Bcl-xL gene expression. We hypothesize that the negative regulation of Bcl-xL transcription by Ikaros contributes to Ikaros'function as a tumor suppressor. The role of CK2 kinase-mediated phosphorylation of Ikaros in regulation of Bcl-xL transcription will be studied. We will test whether constitutive expression of Bcl-xL interferes with Ikaros'tumor suppression in vivo using mice with targeted disruption of Ikaros as a model. These studies will provide the first detailed functional analysis of the signal transduction pathways that control the tumor suppressor function of Ikaros. Our research will provide new and important information on the mechanisms controlling the proliferation of hematopoietic cells and will yield insights into the pathophysiology and treatment of leukemia. PUBLIC HEALTH RELEVANCE: The objective of the proposed study is to understand the mechanism of normal blood formation and immune system development, and changes that lead to development of leukemia. The goal of the proposed project is to identify the function of Ikaros gene. Normal function of Ikaros is essential for normal blood forming and immune system development. Altered activity of the Ikaros gene is associated with the development of childhood acute lymphoblastic leukemia (ALL), infant leukemia and juvenile chronic lymphocytic leukemia. Thus, our results will help to gain insights into the mechanism of normal blood forming and development of leukemia. Further elucidation of the mechanism of the malignant transformation process will aid in providing novel and more effective treatment options for patients with leukemia/lymphoma.